Transmitting system



Aug. 1, 1933. J. B. COLEMAN I 1,920,296

TRANSMITTING SYSTEM Filed Aug. '7, 1926 INVENTOR John 5. 0079mm WITNESSES:

Patented Aug. 1, 1933 1 I UNITED, STA

1,920,296 TRANSMITTING SYSTEM John B. Coleman, Edgewood, Pa., assignor to Westinghouse Electric & Manufacturing Company, a Corporation of Pennsylvania Application August 7, 1926. Serial No. 127,725

2 Claims. (Cl..250-17.)

My invention relates to transmitting systems, and it has particular reference to radio transmitting systems.

One object of my invention is to provide control means for a radio transmitting system comprising an oscillation generator. 7

Another'object of my invention is to provide, in a radio transmission system, control means that will absorb a minimum of energy from the oscillation generator.

Another object of my invention is to provide, in a radio transmitting system, control means that will vary the frequency of the oscillation generator without absorbing an appreciable amount of energy therefrom.

A still further object of my invention is to provide for an oscillation generator, in a radio transmitting system, control means that will not necessarily be subjected to high voltages.

At the present time, there are in use many different types of apparatus for impressing signal variations on the output of a radio transmitting system. In certain of the systems now in use, the amount of energy reaching the plates of the oscillator tubes is varied at signal frequency, in others, the grid bias of the oscillator tubes is caused to vary in accordance with the signal, while, in others, signalling is accomplished by variably absorbing energy directly from the antenna-ground system.

Transmitting systems adapted solely for the radiation of code signals have also been developed, signalling being accomplished by a variation of the frequency of the energy radiated from the one to the other of two definite frequencies, one frequency representing spaces and the other representing characters, such as dots and dashes. To obtain this variation in frequency between definite limits, it has been proposed to provide a portion of the radiating system with a shunt circuit in the nature of an absorption device and to so vary the amount of energy absorbed that the frequency of the radiated wave is changed. Such a system necessarily dissipates a considerable amount of energy, and it is further necessary to provide the absorbing means with heavy insulation against high voltages.

My present invention provides a transmitting system in which the frequency of the radiated energy is controlled by a device which consumes substantially no power. In a specific embodiment, I employ a transmitting system now Known as the master-oscillator type, adding thereto a piezo-electric crystal for controlling the oscillation frequency. In order to impress signal variationson the output of my system, I provide a device which mechanically varies the frequency at which the piezo-electric crystal tends to oscillate, and this, inturn, varies the frequency of the entire master-oscillator.

In order that a complete understanding of the details of my invention may be had, reference is made to the accompanying drawing and to the following description; l I

The single figure of the drawing is a diagrammatic view of a crystal-controlled radio transmitting system embodying a preferred form of my invention. For purposes of explanation, I have shown an oscillation-generating circuit of the type disclosed and claimed in a co-pending application in the name of D. G. Little, Serial 78,115, filed December 29th, 1925, and assigned to the Westinghouse Electric and Manufacturing Company. A thermionic tube 1, preferably of low power, having a grid 2, a plate 3 and a filament 4,'is. pro.- vided with an output circuitcomprising an induce tor 5 and a condenser 6. The input circuit for this tube comprises a piezoeele'ctric crystal 7, shunted by a radio-frequency choke coil 8 in series with a grid biasing battery 9. A-source 10 of filament potential is also provided, as well as a source 12 of plate potential. A second thermionic device 13 having a grid 14, afilament 15 and 'a plate 16, is so arranged that the grid 14 is rss PATENT orFicYE- fl coupled through a condenser 16 to the circuit comprising the inductor 5 and the condenser 6. Between the grid l4and filament 15 of the second thermionic device 13 are connected a radiofrequency choke coil 18 and a grid biasing battery 19, and the tube is. further provided with an output circuit comprising an inductor 20 and a condenser 21. Filament potential for the second tube is supplied by a battery 22, while plate potential may be supplied by a direct-current generator 23. A third thermionic device 24 having a V grid 25, a filament 26 and a plate 27, is coupled to the inductor 20 in the output circuit of the preceding tube, through a small condenser 28. The output circuit of the third thermionic device 24 comprises an inductor 29 shunted by a condenser 30,.and this circuit is coupled through a choke coil 32, to a, radiating. system comprising an antenna 33 and a counterpoise 34. Plate potential for the thermionic device 24 is furnished by a generator 35 in series with a radio-frequency choke coil 36. Filament potential is furnished by a battery 37, while the grid potential is fixed by a battery 38 in series with a radio-frequency choke coil 39.

supporting element 48 in the proper position,

The armature 50' which is determined by trial. ispivotally mounted between a plurality of uprights 53, only one of which appears in the drawing. Adjustable contacts 54 and 55 are provided to limit the upward and downward travel of the armature, and a spring 56 is supplied to hold the armature in the n0n-operative position. A relay winding 57, in series with a battery 53 and a telegraph key 59, serves to alter the position of. the armature in response to signals. As

shown in the drawing the support'48 for the crys tal is conductively connected to the grid of the first thermionic device, while the movable 1118111"- ber 41 isconnected to the filament 4 of the same device.

. In the operation of my device, the upper member 41 carried by the armaturefiil is caused to approach toward, or recede from, the lower member'48 in response to energization of the relay winding 57. The variation of the distance between the member 41 and 48, alters the capacity of the condenser formed thereby. The piezoelectric crystal, being a. part of the dielectric of this condenser, is accordingly subjected to a varying electrostatic field when the members 41 and 48 are moved relatively to each other. Although, at this time, I am not prepared to state the exact theory involved, it is noted that the oscillation frequency of the crystal is varied in accordance with the variation in the spacing of these members. A shift of from500 to 1090 cycles is obtainable with but the slightest movement of the armature; and this small shift is ample to impress signal variations on the high-frequency output, especially when using the type of harmonic generator disclosed in the application of D. G. Little, already referred to.

My invention accordingly provides a keying device that consumes substantially no power. It further provides a device which is safe to use, as the voltages involved need be' no higher than is necessary to secure proper grid bias of the master-oscillator tube.

With careful adjustment, the frequency shift of the radiated wave is exact, and it may be we determined with a high degree of accuracy. A transmitting system equipped with my invention causes, substantially no interference outside of the frequency it is set to radiate, as harmonics are noticeably absent.

For the transmission of signals on ultra-high frequencies, my invention has proved of great value, as it obviates the use of keyingdevices which cause irregular shifts in radiated frequency, and key thumps.

Although I have illustrated and described a single specific embodiment of my invention, it is not my intention to be restricted thereto, only such limitations being contemplated as are iniposed by the priorart or expressed in the appended claims.

I claim as my invention:

1. A telegraph keying device comprising a piezo-electric crystal, supporting means therefor, movable means associated therewith, means for adjusting the space relationship of the .movable means to the crystal, and means, responsive to signal impulses, for repeatedly altering said relationship. v I

2. A telegraph keying device, having, in combination, a piezo electric crystal, adjustable supporting means therefor, an element movable in response to signals associated therewith,- and means for limiting the travel of said movable element.

- JOHN B. COLEMAN. 

